Prevention of siliceous deposition from steam



A. c. SCHUBRING ETAL 2,595,490

PREVENTION OF SILICEZOUS DEPOSITION FROM STEAM Filed Jan. 4, 1945 CONDENSER May 6, 1952 RATE OF WATER INSOLUBLE slo DEPOSITION R E o5# W I M 70 2 G mm NET l .mm F R 5:.- E 05 w Rm 8 DR 5 I J O O O 0 0 0 0 0 0 0 0 0 0 O 0 O M u w w. w w w. 2 n7 uZuF Z uhn Patented May 6, 1952 PREVENTION OF SILICEOUS DEPOSITION FROM STEAM Arthur C. Schubring, Trenton, and Lyman W. Jillson, Detroit, Mich., assignors to Wyandotte Chemicals Corporation, Wyandotte, Mich., a

corporation of Michigan Application January 4, 1945, Serial No. 571,294

This invention relates to the prevention of the formation of a water-insoluble deposit, consisting essentially of silica, on surfaces of heat engines and apparatus that are contacted by steam in which such silica containing matter is entrained. The formation of a hard, gray colored deposit of siliceous material in heat absorbing machines such as steam turbines and heat exchangers, has constituted a problem of long standing in the art of steam practice. Such deposit cannot be removed from the surfaces upon which it adheres by means of water washing, but some more severe chemical or mechanical treatment is necessary.

The deposition of a hard, tenacious silica containing deposit on the blading of steam turbines has been a particularly severe problem in the art because as the deposit builds up, the clearance between the blades is thus reduced, causing a throttling action of the steam with resultant heat loss and inefiiciency of operation requiring a periodic shutting down of the turbine and washing out with caustic soda or other solvent or by mechanical cleaning.

Much effort has heretofore been expended in the solution of this problem, most of it directed toward the elimination of silica in the boiler feed water. However, even where silica in the feed water has been reduced to as low as 2 parts per million, the deposition of the water-insoluble siliceous material still occurs. It has been stated by F. Spillner (Die Chemische Fabrik, vol. 13, No. 22, Nov. 2, 1940) that the amount of salt carryover in steam is entirely independent of the salt content of the boiler water and that the deposition of silica in the turbine is one of the worst manifestations of salt deposition.

We have made the discovery that regardless of the amount of siliceous matter entrained in' the steam, there is a critical temperature range in which the hard, water-insoluble deposit is formed. Accordingly, and on the basis of this discovery, our invention has solved the indicated problem, not by seeking to eliminate silica and related siliceous material from the feed water, but by preventing the introduction and use of steam containing entrained siliceous matter over the critical temperature range wherein the deposit occurs. Briefly, we accomplish this objective by by-passing from the machine or apparatus the steam containing the entrained siliceous material,- and over the critical temperature 2 Claims. (01. 122-459) range in which the water-insoluble deposit has I 2 al objectives and to enable any person skilled in the art readily to understand and practice the invention, the following full and concise description and annexed drawing set forth the best mode in which we have contemplated applying the principle of our invention.

In the drawing, Fig. 1 is a flow diagram representing a steam power system into which the principle of our invention has been incorporated.

In the drawing, Fig. 2 is a chart illustrating the critical temperature range over which the hard, water-insoluble silica containing deposit occurs with respect to the temperature of the steam which carries it.

Referring to Fig. 2, it will be seen that the rate of Water-insoluble silica deposition is plotted against the steam temperature. Such rate of deposition, it will be seen, is the greatest in the temperature range between 450 and 540 F. Above and below this range, there is some formation of deposit, but such deposit is not here deemed material or of importance because it is of a water-soluble material, and in the case of a machine or apparatus wherein the heat extracted from the steam is suflicient to produce condensation, viz. to form west steam, the water-soluble deposit is automatically washed clean and presents no difficulty. Thus it will be seen, that over the critical temperature range or zone of 450 to 540 F., the undesirable hard, water-insoluble deposit of siliceous material occurs. Thus, if steam is cooled through the critical temperature range of 450-540 F. in a heat adsorbing machine, water-insoluble siliceous deposits will form on the interior surfaces thereof.

In Fig. 1, steam flows from a boiler I through line 3, superheater 4 and line 5 to the turbine [0. Turbine l D is of the multi-stage type and a bafile wall II is shown placed between those stages in the turbine at a point where the steam on giving up heat energy and after passing through the initial stages of the turbine, corresponds to a temperature approaching 540 F. and 125 lbs. pressure. At this point and just in advance of the baffle wall H, the steam is led off from the turbine ID through the line l2 to the silica precipitator l3 wherein the hard, water-insoluble deposit is permitted to occur. This silicia precipitator l3 may suitably be any sort of steam machine or apparatus wherein the formation of the deposit is immaterial or of no consequence, such as for example, a reciprocating engine or a low velocity chamber containing relatively a 3 moval of the water-insoluble deposit in precipitator I3, is introduced through line H to the opposite side of the baflle wall II at 438 F. and 123 lbs. pressure where it passes through the subsequent stages of the turbine l0. Thus, it will be seen, that the possibility of formation of undesired deposit in the turbine I0 is eliminated.

Other modes of applying the principle of our invention, in addition to the one herein and above described and illustrated in detail, may be employed, provided the step or steps stated by any of the following claims or the equivalent of such step or steps be utilized.

We, therefore, particularly point out and distinctly claim as our invention and discovery:

1. A method of purifying superheated steam, which comprises introducing superheated steam at a temperature of at least 540 F. into a container for removing impurities therefrom, cooling the steam in the container to a temperature at least as low as 450 F. while maintaining the steam in a superheated condition, and removing the purified superheated steam from the container.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,666,523 Bailey Apr. 17, 1928 2,028,504 Egloif Jan. 21, 1936 2,149,160 Block et a1. Feb. 28, 1939 2,155,039 Eglofi Apr. 18, 1939 2,194,151 Rieger et al Mar. 19, 1940 2,298,242 Wegmann Oct. 6, 1942 

2. A METHOD OF PURIFYING DRY SUPERHEATED STEAM, WHICH COMPRISES HEATING STEAM ABOVE 540* F., AND THEREAFTER COOLING SAID STEAM THROUGH THE TEMPERATURE RANGE OF 540*-450* C. TO PRECIPI- 